Roughly chop the onion and zucchini and sautè in a pan drizzled with olive oil for 3-4 minutes. Add salt, black pepper and fish stock and let cook for a few minutes, until the zucchini becomes tender (there should be still some liquid left in the pan).
Transfer the vegetables to a blender and add the mint leaves and the cream. Blend until creamy and smooth. Add more stock if necessary then set aside.
In the same pan where you cooked the vegetables, add more olive oil and the minced garlic and sautè at medium heat. When the garlic starts to fry, add the shrimps. Season with salt, pepper, lemon juice and chili flakes and cook 3-4 minutes on each side, until lightly golden. Then set aside to keep warm.
Meanwhile, in a large pot bring to boil salted water then cook the Paccheri pasta al dente (follow the package instruction for the right timing).
Transfer the zucchini sauce back in the pan with the shrimps, then drain the cooked pasta and add it to the sauce. Sautè for 1-2 minutes to blend the flavors and serve.